LDC CD103⁺, LDC CD24⁺, and LMΦ CD64⁺ cells all express high levels of APRIL and BAFF. (A) Representative flow cytometry plots comparing the expression of APRIL protein in lung APC subsets. (B) Cumulative data comparing the mean fluorescence intensity (MFI) of APRIL expression. Three independent experiments are shown here with three mice per experiment. Statistical comparisons are made to SpDCs. (C) Immunofluorescent analysis of APRIL expression on sorted, LDC CD103⁺, LDC CD24⁺, LMφ CD64⁺, and SpDCs where DAPI is shown in blue, CD11c in green, and APRIL in red. Bar, 10 µm. (D) qRT-PCR of mRNA isolated from flow-sorted LDC CD103⁺, LDC CD24⁺, LMφ CD64⁺, MLN DCs, and SpDCs comparing the expression of mAPRIL (top) and mBAFF (bottom). Data are normalized to GAPDH and expressed in relative units. (E and F) Flow-sorted LDC CD103⁺ or LDC CD24⁺ were cultured with CD43^negCD19⁺IgM⁺ B cells in the absence or presence of TACI-Fc antibody added on culture days 0 and 3. (E) Representative flow cytometry plots. (F) Cumulative data from two independent experiments with seven mice pooled per experiment. (G and H) Flow cytometric analyses showing the effect of blocking IL-10 on LDC-induced IgA CSR. Flow-sorted LDC CD103⁺ or LDC CD24⁺ were cultured with naive B cells in the absence or presence of α-IL-10 neutralizing antibody added on culture days 0 and 3, and IgA⁺ B cells were quantified. (G) Representative flow cytometry plots. (H) Cumulative data from two independent experiments with seven mice pooled per experiment. (I–K) Flow-sorted LMφ CD64⁺ were cultured with CD43^negCD19⁺IgM⁺ B cells in the indicated conditions, and IgA⁺ B cells were quantified. (I) Representative flow cytometry plots. (J) Cumulative data from three different experiments with seven mice pooled per experiment. Statistical comparisons are made to LMφ CD64⁺ alone. (K) Cumulative data from two individual experiments with six mice pooled per experiment. Statistical comparisons are made to LMφ CD64⁺ alone. **, P < 0.01; ***, P < 0.001.